Enhanced electrochemical stability of carbon quantum dots-incorporated and ferrous-coordinated polypyrrole for supercapacitor

Agricultural and industrial wastes applied on the high performance energy storage devices

Driven by population growth, the destruction of the environment and the energy demand continue to increase dramatically. This study uses garlic skin and carbon fiber from agricultural and industrial wastes to prepare energy storage devices. Carbon quantum dots (CQDs) were obtained from garlic skin using high-temperature pyrolysis. The specific capacitance of the gel electrolyte could be effectively increased with a small number of CQDs doping. A methylcellulose-based carbon fiber-electrode was prepared by grinding and depositing the industrial recycled carbon fiber onto a biodegradable methylcellulose substrate. The methylcellulose-based recycled carbon fiber-electrode has the highest specific capacitance, energy density, and power density, which are 155 F/g, 10 Wh/kg, and 4047 W/kg, respectively, at a scan rate of 0.02 V/s, and demonstrates excellent performance, such like high specific capacitance, low internal resistance as well as rapid charge and discharge characteristics, which may have potential to replace the expensive carbon nanotubes and graphenes. The electrodes were made from recycled carbon fiber, the gel electrolyte with garlic CQDs, and a separator assembled into a sandwich structure to form supercapacitors. The capacity retention rate of the supercapacitor still retained 96 % of its initial value after 2000 cycles of charge and discharge testing at a constant current of 0.20 mA. This demonstrates the supercapacitor prepared in this study with competitive power density, energy density, high rate capability, and excellent life cycle stability by combining the garlic skin and carbon fiber from agricultural and industrial wastes, highlighting the enormous potential of agricultural and industrial wastes for energy storage applications.

Polymer Composites with Quantum Dots as Potential Electrode Materials for Supercapacitors Application: A Review

Owing to the nanometer size range, Quantum Dots (QDs) have exhibited unique physical and chemical properties which are favourable for different applications. Especially, due to their quantum confinement effect, excellent optoelectronic characteristics is been observed. This considerable progress has not only uplifted the singular usage of QDs, but also encouraged to prepare various hybrid materials to achieve superior efficiency by eliminating certain shortcomings. Such issues can be overcome by compositing QDs with polymers. Via employing polymer composite with QDs (PQDs) for supercapacitor applications, adequate conductivity, stability, excellent energy density, and better specific capacitance is been achieved which we have elaborately discussed in this review. Researchers have already explored various types of polymer nanocomposite with different QDs such as carbonaceous QDs, transition metal oxide/sulphide QDs etc. as electrode material for supercapacitor application. Synthesis, application outcome, benefits, and drawbacks of these are explained to portray a better understanding. From the existing studies it is clearly confirmed that with using PQDs electrical conductivity, electrochemical reactivity, and the charge accumulation on the surface have prominently been improved which effected the fabricated supercapacitor device performance. More comprehensive fundamentals and observations are explained in the current review which indicates their promising scopes in upcoming times.

Effect of oxygen vacancies on the electronic structure and electrochemical performance of MnMoO4: computational simulation and experimental verification

Porous nanopetals of MnMoO4 with oxygen vacancies (MnMoO4–OV) were synthesized and deliver preferable energy storage performance.

Carbon-Based Quantum Dots for Supercapacitors: Recent Advances and Future Challenges

Carbon-based Quantum dots (C-QDs) are carbon-based materials that experience the quantum confinement effect, which results in superior optoelectronic properties. In recent years, C-QDs have attracted attention significantly and have shown great application potential as a high-performance supercapacitor device. C-QDs (either as a bare electrode or composite) give a new way to boost supercapacitor performances in higher specific capacitance, high energy density, and good durability. This review comprehensively summarizes the up-to-date progress in C-QD applications either in a bare condition or as a composite with other materials for supercapacitors. The current state of the three distinct C-QD families used for supercapacitors including carbon quantum dots, carbon dots, and graphene quantum dots is highlighted. Two main properties of C-QDs (structural and electrical properties) are presented and analyzed, with a focus on the contribution to supercapacitor performances. Finally, we discuss and outline the remaining major challenges and future perspectives for this growing field with the hope of stimulating further research progress.

In situ green synthesis of highly fluorescent Fe2 O3 @CQD/graphene oxide using hard pistachio shells via the hydrothermal-assisted ball milling method

In this study, highly photoluminescent and photocatalytic Fe₂ O₃ @carbon quantum dots/graphene oxide nanostructures were synthesized using ball milling-assisted hydrothermal synthesis with hard pistachio shells. Different analyses, such as X-ray diffraction, energy dispersive X-ray spectroscopy, and Fourier transform infrared spectroscopy were used to study the product structure. Scanning electron microscopy and transmission electron microscopy images were used to study product size and morphology. Optical properties of the as-synthesized nanomaterials were investigated using ultraviolet-visible light and photoluminescence analyses. To increase photoluminescence intensity, ethylene diamine tetraacetic acid, polyethylene glycol, polyvinylpyrrolidone, and acetylacetonate anions were used to modify the product surface. Thermal stability of the product was studied using thermal gravimetric analysis. Finally, photocatalytic activity and surface adsorption of the product were investigated; the produce was found to be highly photoluminescent with high photocatalytic and surface activities.

A high-performance asymmetric supercapacitor electrode based on a three-dimensional ZnMoO4/CoO nanohybrid on nickel foam

A two-step hydrothermal route was employed to fabricate a ZnMoO₄/CoO nanohybrid supported on Ni foam. The ZnMoO₄/CoO nanohybrid shows a three-dimensional criss-crossed structure. The specific surface area is enhanced from 45 m² g^-1 of ZnMoO₄ to 67 m² g^-1 of the ZnMoO₄/CoO nanohybrid. Furthermore, the existence of electroactive CoO is in favor of reducing the charge transport resistance. The ZnMoO₄/CoO nanohybrid electrode possesses a high capacitance of 4.47 F cm^-2 at 2 mA cm^-2, which is much higher than those of ZnMoO₄ (1.07 F cm^-2) and CoO (2.47 F cm^-2). The ZnMoO₄/CoO nanohybrid electrode also exhibits an ultrahigh cycling stability with 100.5% capacitance retention after 5000 cycles at 20 mA cm^-2. In addition, an asymmetric all-solid-state supercapacitor was assembled using the ZnMoO₄/CoO nanohybrid as the positive electrode and exfoliated graphite carbon paper as the negative electrode. The asymmetric supercapacitor exhibits a superior energy density of 58.6 W h kg^-1 at a power density of 800 W kg^-1 and a considerable cycling stability with 81.8% capacitance retention after 5000 cycles at 5 A g^-1. The ZnMoO₄/CoO nanohybrid demonstrates its tremendous advantages and possibilities as a positive electrode material in energy storage applications. Moreover, for a better understanding of the electrochemical behavior, a combined study of experimental measurements and density functional theory calculations is also applied to illustrate the high-performance of the ZnMoO₄/CoO nanohybrid.

Activation of carbon fiber for enhancing electrochemical performance

Carbon fiber sequentially undergoes thermal activation, electrochemical oxidation activation, electrochemical reduction activation and a secondary thermal activation process to form a highly activated carbon fiber electrode material.